Using strings to drill down into objects

Folks,
I’m writing a reporting application where I’m passing in an array
of
method calls to populate a table

e.g.

# lambda function to drill down object hierarchy
drill_down = lambda do |obj, method_name|
                      o ||= obj
                      method_name.split('.').each {|m| o = o.send(m) 

if
o.respond_to?(m)}
o
end

methods = [‘lookup1.code’, ‘lookup1.name’]

report_value = drill_down.call(my_object_with_lookups, methods)

I’m sure there is a better “Ruby” way of doing this. Can someone offer
some advice?

Ross D.
Developer
Data Management & Reporting
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Ross X Dawson wrote:

report_value = drill_down.call(my_object_with_lookups, methods)
I’m not sure what your intent is, but I guess this code won’t work.

First, unless you define it before creating the lambda, “o” won’t exist
in its binding, so you can’t call o ||= obj. Second, you pass an array
of method names to your lambda as a second parameter, on which #split
isn’t defined.

You could state instead:

method_name.each{|name| name.split{|part| … } }

but then, “part” would take the value “lookup1”, “code”, “lookup1”
again, and “name” in that order. I highly doubt you want this.

However, AFAIK you’re right that o.send(m, *args) is the way to call an
arbitrary named method on an object.

mortee

mortee wrote:

Ross X Dawson wrote:

# lambda function to drill down object hierarchy
drill_down = lambda do |obj, method_name|
                      o ||= obj
                      method_name.split('.').each {|m| o = o.send(m) if

o.respond_to?(m)}
o
end

method_name.each{|name| name.split{|part| … } }

Sorry, that should read

method_name.each{|name| name.split(’.’).each{|part| … } }

On Oct 11, 8:32 am, mortee [email protected] wrote:

report_value = drill_down.call(my_object_with_lookups, methods)

I’m not sure what your intent is, but I guess this code won’t work.

First, unless you define it before creating the lambda, “o” won’t exist
in its binding, so you can’t call o ||= obj.

Are you sure about that?

[email protected]:~$ irb
irb(main):001:0> x ||= 7
=> 7
irb(main):002:0> x
=> 7

Brian A. wrote:

Are you sure about that?

[email protected]:~$ irb
irb(main):001:0> x ||= 7
=> 7
irb(main):002:0> x
=> 7

Sorry, you’re right. I’ve never tried this actually on an undefined
local variable - and I guessed it would first try to evaluate x, which
would raise an exception. Thanks for pointing that out, I’m happy to
have learnt it (:

mortee

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